21 August 2013

Wei-Yin Chen and a Disturbing Late-Game Trend

After another frustrating Orioles' loss, Wei-Yin Chen takes the mound tonight in hopes of getting the O's back on track. But something strange is going on with Chen. Despite missing about two months of the season with a strained oblique, he has still arguably been the team's best pitcher. Only two relievers, Darren O'Day and Tommy Hunter, have a lower ERA than Chen's 3.23, and although Chen's strikeouts per nine are down by about 1.5, he's walking fewer batters and doing a better job of keeping the ball in the ballpark.

But that's not the weird part. What's odd is how Chen has been completely falling apart in late-game situations. Let's explore those struggles further.

First of all, Chen has only pitched 94.2 innings this season and this is just his second major league season, so even though what follows are his career stats, they're limited. In his brief career, Chen is pretty good in the early and middle innings. After the fifth, though, things can get dicey. Here are the major league average batting lines in three-inning snippets:

But the trouble for Chen really starts in the sixth inning. In 34.1 career innings pitched in the sixth, Chen has allowed batters to hit .296/.340/.479 against him -- far and away his worst of the first six innings. Things only get worse after that.

Let's dig a little deeper. As batters face opposing pitchers more times in the same game, their stats improve a bit. They do a little better in their second plate appearance, and even better in the third appearance. The same isn't true for the fourth(-plus) plate appearance, though if a pitcher is still in the game by then, he's probably doing a pretty good job and/or has filthy stuff that night. Here are the major league averages this season:

Opposing batters' slugging percentage against Chen in that third plate appearance is very high, and things don't get any better if he manages to stick around for a fourth time through a lineup.

As you would expect, those similar struggles are reflected in Chen's pitch count numbers. On pitches 1-75, Chen holds opposing batters around (on pitches 1-25) or below (on pitches 26-50 and 51-75) the MLB average batting line for those amounts of pitches. But after pitch 75, Chen has some issues:

So is Chen getting tired? That's one possibility, especially since Chen pitched in Japan, where six-man rotations are popular. In his career, Chen pitches better after more days' rest, but then again, not every pitcher who pitched in Japan falls apart later in games, either.

But is he also not throwing the right pitches? Are his pitches not moving the same? Is there some amount of unluckiness and/or small sample size issues? All of the above, most likely.

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Chen throws two fastballs (a four-seamer and a sinker), a slider, and a change-up. He also occasionally mixes in a curveball. Overall, Chen throws his four-seam fastball the most of all his pitches -- nearly 57% of the time. That pitch is followed by the slider (14.4%), change-up (12.8%), and sinker (9.7%). (All numbers via Brooks Baseball.)

He starts out most games throwing lots of four-seamers, but that number drops after the first few innings and sits a bit above 50%. Instead of those four-seamers, he throws more sliders and change-ups.

It's possible that those extra offspeed pitches are getting him into trouble.

In terms of velocity, Chen's numbers are holding steady. His fastball velocity to start the game is about 92 mph, and that average doesn't drop below 91.67 in any of the following innings. His average fastball velocity of 91 mph is also identical to last season's.

Chen does a pretty good job of maintaining the horizontal movement on just about all of his pitches as the game goes on, but the same isn't true for the vertical movement on his pitches. His four-seam movement is consistent, but his sinker and slider both start to lose some movement in the middle innings. The issues with the slider are probably the most concerning, because that's the pitch of Chen's that moves the least.

One other note: Overall, the left-handed Chen is better against left-handed batters. Here are his career splits vs. righties and lefties:

vs. RH: .258/.309/.420
vs. LH: .221/.277/.378

(Note: Average major league batting line in 2013 is .254/.318/.398.)

He has no problem getting swings and misses against lefties in the early innings, but lefties start making more contact as the game goes on.

For some reason, Chen starts out games against righties by not getting as many whiffs, but he starts getting more in the middle innings before they start decreasing again.

Some pitchers simply are not as effective as they go multiple times through a lineup. Maybe if Chen were more of a strikeout pitcher, he wouldn't have as much trouble in the sixth inning and later. But while Chen's late-game issues are holding him back from being an even better pitcher, he's still pretty good and one of the best rotation options the O's have had in years.

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Jon Shepherd - founder@CamdenDepotStarted Camden Depot in the summer of 2007. By day, a toxicologist and by night a baseball analyst. His work is largely located on this site, but may pop up over at places like ESPN or Baseball Prospectus.

Matt Kremnitzer - editor@mattkremnitzerMatt joined Camden Depot before the 2013 season. He previously wrote about the Orioles and D.C. sports at Krem's Sports.

Nate Delong - writer, assistant editor@OriolesPGNate created and wrote for Orioles Proving Ground prior to joining Camden Depot in the middle of 2013. His baseball resume includes working as a scorer for Baseball Info Solutions and as a Video Intern for the Baltimore Orioles. His actual resume is much less interesting.

Matt Perez - writerMatt joined Camden Depot after the 2013 season. He is a data analyst/programmer in his day job and uses those skills to write about the Orioles and other baseball related topics.

Joe Reisel - writerJoe has followed the Norfolk Tides now for 20 seasons. He currently serves as a Tides GameDay datacaster for milb.com and as a scorer for Baseball Info Solutions (BIS). He is computer programmer/analyst by day.

Ryan Romano - writer@triple_r_Ryan writes about the Orioles on Camden Depot and about all baseball at Beyond the Box Score. He previously wrote on Birds Watcher and on Camden Chat that one time.